Tunable coupler for superconducting Xmon qubits: Perturbative nonlinear model

Geller, Michael R.; Donate, Emmanuel; Chen, Yu; Fang, Michael; Leung, Nelson; Neill, C.; Roushan, P.; Martinis, John M.

doi:10.1103/physreva.92.012320

Cited by 82 publications

(76 citation statements)

References 28 publications

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“…In a superconducting device, the qubits are built with a Josephson tunnel element, an inductance and a capacitor, 11 whereas local operations and measurements are performed by coupling the qubit to a resonator. 12 The interactions can be designed using lithographic techniques by jointly coupling two qubits via a capacitor 13 or an inductance, 14 and can be modelled via an effective two-body Hamiltonian P α J α σ α σ α 15,16 where σ α are the Pauli matrices. Because of the flexibility in wiring the pairwise interactions among the qubits, it is possible to arrange them in a planar graph structure, namely a collection of vertices and links, in which the vertices correspond to the qubits and the links correspond to the two-body interactions between them.…”

Section: Introductionmentioning

confidence: 99%

Quantum gate learning in qubit networks: Toffoli gate without time-dependent control

2016

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We put forward a strategy to encode a quantum operation into the unmodulated dynamics of a quantum network without the need for external control pulses, measurements or active feedback. Our optimisation scheme, inspired by supervised machine learning, consists in engineering the pairwise couplings between the network qubits so that the target quantum operation is encoded in the natural reduced dynamics of a network section. The efficacy of the proposed scheme is demonstrated by the finding of uncontrolled four-qubit networks that implement either the Toffoli gate, the Fredkin gate or remote logic operations. The proposed Toffoli gate is stable against imperfections, has a high fidelity for fault-tolerant quantum computation and is fast, being based on the non-equilibrium dynamics. INTRODUCTIONComputational devices based on the laws of quantum mechanics hold promise to speed up many algorithms known to be hard for classical computers. 1 The implementation of a full-scale computation with existing technology requires an outstanding ability to maintain quantum coherence (i.e., isolation from the environment) without compromising the ability to control the interactions among the qubits in a scalable way. Among the most successful paradigms of quantum computation, there is the 'circuit model', in which the algorithm is decomposed into an universal set of single-and two-qubit gates, 2 and, to some extent, the so-called adiabatic quantum computation (AQC), 3 in which the output of the algorithm is encoded in the ground state of an interacting many-qubit Hamiltonian. A different approach 4 is based on the use of always-on interactions, naturally occurring between physical qubits, to accomplish the computation. Compared with the circuit model, this scheme has the advantage of requiring minimal external control and avoiding the continuous switch off and on of the interactions between all but two qubits, whereas compared with AQC it has the advantage of being faster, being based on the non-equilibrium evolution of the system. Quantum computation with always-on interactions is accomplished by combining the natural couplings with a moderate external control, e.g., with a smooth shifting of Zeeman energies, 5 via feed-forward techniques, 6 using measurement-based computation 7 or quantum control. 8,9 Most of these approaches are based on the assumption that the natural couplings are fixed by nature and not tunable, whereas local interactions can be modulated with external fields. However, the amount of external control required can be minimised if the couplings between the qubits can be statically tuned 10 -e.g., during the creation of the quantum device.The recent advances in the fabrication of superconducting quantum devices has opened up to the realisation of interacting quantum networks. In a superconducting device, the qubits are built with a Josephson tunnel element, an inductance and a

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Section: Introductionmentioning

confidence: 99%

Quantum gate learning in qubit networks: Toffoli gate without time-dependent control

2016

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“…A local optimization algorithm is then carried out for a corresponding reduced set of parameters; see discussion in the text. It is worth noting that the majority of the network is made up of ZZ interactions, which is obtainable in superconducting circuits, among others, as shown by Geller et al [47]. Additionally, McKay et al showed that it was possible to obtain (XX + Y Y ) interactions in a superconducting circuit [48], lending itself nicely for the interactions between the second and third qubits of this network.…”

Section: Resultsmentioning

confidence: 85%

Quantum arithmetics via computation with minimized external control: The half-adder

2018

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The while-you-wait computing paradigm combines elements of digital and analog quantum computation with the aim of minimizing the need of external control. In this architecture the computer is split into logic units, each continuously implementing a single recurring multigate operation via the unmodulated Hamiltonian evolution of a quantum many-body system. Here we use evolutionary algorithms to engineer such many-body dynamics, and develop logic units capable of continuously implementing a quantum half-adder in a time-independent four-qubit network, where qubits are coupled with either Ising or Heisenberg interactions. Our results provide a step for the development of larger modules for full quantum arithmetics.

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“…However, their coupling is determined by the fixed geometric arrangement of the resonators, resulting in a static coupling g bs that can not be switched off. In order to make the coupling switchable, different schemes have been proposed theoretically [23,24] and implemented experimentally [13][14][15]. All these proposals are based on superconducting rings acting as tunable couplers (cf.…”

Section: Boson Sampling With Superconducting Circuitsmentioning

confidence: 99%

Proposal for Microwave Boson Sampling

et al. 2016

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The first post-classical computation will most probably be performed not on a universal quantum computer, but rather on a dedicated quantum hardware. A strong candidate for achieving this is represented by the task of sampling from the output distribution of linear quantum optical networks. This problem, known as boson sampling, has recently been shown to be intractable for any classical computer, but it is naturally carried out by running the corresponding experiment. However, only small scale realizations of boson sampling experiments have been demonstrated to date. Their main limitation is related to the non-deterministic state preparation and inefficient measurement step. Here, we propose an alternative setup to implement boson sampling that is based on microwave photons and not on optical photons. The certified scalability of superconducting devices indicates that this direction is promising for a large-scale implementation of boson sampling and allows for more flexible features like arbitrary state preparation and efficient photon-number measurements.

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Tunable coupler for superconducting Xmon qubits: Perturbative nonlinear model

Cited by 82 publications

References 28 publications

Quantum gate learning in qubit networks: Toffoli gate without time-dependent control

Quantum gate learning in qubit networks: Toffoli gate without time-dependent control

Quantum arithmetics via computation with minimized external control: The half-adder

Proposal for Microwave Boson Sampling

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